By way of background, in some applications analog radio frequency (RF) systems need to rapidly identify signals over a wide frequency range in order to respond to those signals. For example, this may be important for object recognition in a radar (e.g., microwave) application, as well as to identify interfering signals across an operating frequency band for interference mitigation purposes. Depending on the particular application, various parameters which may be important in an RF signal identification configuration may include speed, accuracy, weight constraints, and cost.
One conventional approach to signal identification is called a folded receiver. A wideband antenna signal is divided N ways, and N RF tuners down-convert a section of the spectrum to a common intermediate frequency (IF), so that each section of the spectrum may be superimposed and monitored by a single analog-to-digital converter (ADC). The ambiguity of the frequency of a super-imposed signal is resolved by using an RF power meter after each tuner.
Such conventional RF signal identification approaches may suffer from certain drawbacks. One potential drawback is that the bandwidth of this type of system may be relatively limited by the analog RF components. Furthermore, the size, weight, and power (SWaP) of such devices may be prohibitive in certain applications.
Some Extremely High Frequency (EHF) communications systems (e.g., 30 to 300 GHz) use optical signal processing components to help address the bandwidth constraints of RF signal processing. An advantage of such systems is the ability to transmit EHF signals from a remote location without the degradation of the signal incumbent in RF applications.
One particularly advantageous approach is set forth in U.S. Pat. No. 8,842,992 to Middleton et al., which is assigned to the present Assignee and is hereby incorporated herein in its entirety by reference. Middleton et al. is directed to a communications device which includes a transmitter device having an optical source configured to generate an optical carrier signal, a first E/O modulator coupled to the optical source and configured to modulate the optical carrier signal with an input signal having a first frequency, and a second E/O modulator coupled to the optical source and configured to modulate the optical carrier signal with a reference signal. The communications device includes an optical waveguide coupled to the transmitter device, and a receiver device coupled to the optical waveguide and including an O/E converter coupled to the optical waveguide and configured to generate an output signal comprising a replica of the input signal at a second frequency based upon the reference signal.
Despite the advantages of such systems, further developments may be desirable in certain applications.